EP0717644B1 - Circuits de formation d'impulsion - Google Patents

Circuits de formation d'impulsion Download PDF

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Publication number
EP0717644B1
EP0717644B1 EP92910606A EP92910606A EP0717644B1 EP 0717644 B1 EP0717644 B1 EP 0717644B1 EP 92910606 A EP92910606 A EP 92910606A EP 92910606 A EP92910606 A EP 92910606A EP 0717644 B1 EP0717644 B1 EP 0717644B1
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EP
European Patent Office
Prior art keywords
thermistor
storage device
energy
energy storage
medical instrument
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Expired - Lifetime
Application number
EP92910606A
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German (de)
English (en)
Other versions
EP0717644A4 (fr
EP0717644A1 (fr
Inventor
Carlton B. Morgan
Daniel Yerkovich
Donald C. Maier
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Physio Control Inc
Original Assignee
Physio Control Inc
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Publication date
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Publication of EP0717644A4 publication Critical patent/EP0717644A4/fr
Publication of EP0717644A1 publication Critical patent/EP0717644A1/fr
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Publication of EP0717644B1 publication Critical patent/EP0717644B1/fr
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    • A—HUMAN NECESSITIES
    • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61N—ELECTROTHERAPY; MAGNETOTHERAPY; RADIATION THERAPY; ULTRASOUND THERAPY
    • A61N1/00—Electrotherapy; Circuits therefor
    • A61N1/18—Applying electric currents by contact electrodes
    • A61N1/32—Applying electric currents by contact electrodes alternating or intermittent currents
    • A61N1/38—Applying electric currents by contact electrodes alternating or intermittent currents for producing shock effects
    • A61N1/39—Heart defibrillators
    • A61N1/3906—Heart defibrillators characterised by the form of the shockwave
    • A61N1/3912—Output circuitry therefor, e.g. switches
    • A—HUMAN NECESSITIES
    • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61N—ELECTROTHERAPY; MAGNETOTHERAPY; RADIATION THERAPY; ULTRASOUND THERAPY
    • A61N1/00—Electrotherapy; Circuits therefor
    • A61N1/18—Applying electric currents by contact electrodes
    • A61N1/32—Applying electric currents by contact electrodes alternating or intermittent currents
    • A61N1/38—Applying electric currents by contact electrodes alternating or intermittent currents for producing shock effects
    • A61N1/39—Heart defibrillators
    • A61N1/3904—External heart defibrillators [EHD]
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01K—MEASURING TEMPERATURE; MEASURING QUANTITY OF HEAT; THERMALLY-SENSITIVE ELEMENTS NOT OTHERWISE PROVIDED FOR
    • G01K1/00—Details of thermometers not specially adapted for particular types of thermometer
    • G01K1/16—Special arrangements for conducting heat from the object to the sensitive element
    • G01K1/18—Special arrangements for conducting heat from the object to the sensitive element for reducing thermal inertia
    • A—HUMAN NECESSITIES
    • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61N—ELECTROTHERAPY; MAGNETOTHERAPY; RADIATION THERAPY; ULTRASOUND THERAPY
    • A61N1/00—Electrotherapy; Circuits therefor
    • A61N1/18—Applying electric currents by contact electrodes
    • A61N1/32—Applying electric currents by contact electrodes alternating or intermittent currents
    • A61N1/38—Applying electric currents by contact electrodes alternating or intermittent currents for producing shock effects
    • A61N1/39—Heart defibrillators
    • A61N1/3906—Heart defibrillators characterised by the form of the shockwave

Definitions

  • This invention relates generally to circuits for forming electrical pulses. More specifically, it relates to circuits for forming such pulses with a determined amplitude, duration, and shape.
  • RLC circuits Electrical pulses have traditionally been shaped using resistors, capacitors, and inductors, so-called RLC circuits, to form pulses having desired rise and fall patterns, amplitudes, and duration.
  • RLC circuits One disadvantage of such prior art circuits, particularly when pulses of relatively large voltages or currents are required, has been the size and weight of the components required. As a consequence of the size and weight of such prior art RLC circuits, the latter are not adapted for use in relatively small pieces of equipment or where the total weight of the piece of equipment must be minimized. For instance, to the extent the weight and size of the pulse-forming circuits in a defibrillator can be reduced, its portability and hence utility will be increased.
  • the invention utilizes a temperature sensitive resistor, i.e. a thermistor, connected between or across a switched source and a load to shape the electrical pulse supplied to the load.
  • the temperature/resistance characteristics of the resistor are selected so that the shape of the pulse varies in a predetermined manner as a function of the temperature of the resistor.
  • the load can be the transthoracic impedance of a person requiring defibrillation.
  • FIGURE 1 illustrates a first embodiment of the circuit of the present invention in schematic form.
  • This circuit includes a DC source 2 having its positive terminal connected through a first normally opened switch 4 to one side of a capacitor 6, the other side of which is connected to the negative terminal of the source 2.
  • a second normally opened switch 8 Connected in parallel with the capacitor 6 is a second normally opened switch 8, a thermistor 10, and a load represented by a resistive element 12.
  • Thermistor 10 is a self-heating thermally active resistive device. Thermistor 10 is selected to have a negative temperature coefficient so that its resistance will decrease as its temperature rises.
  • the load represented by element 12 typically does not form part of the circuit of the present invention, and is shown in the FIGURES merely to illustrate the manner in which the present circuit is coupled with a resistive load.
  • thermistor 10 In an exemplary embodiment of the invention, three series-connected thermistors of the type manufactured by Keystone Carbon Company of St. Mary's Pennsylvania 15857 and identified by model No. CL-70 may be satisfactorily used as thermistor 10. Also in this embodiment, capacitor 6 is a 37.5mF capacitor and about a 4,200 volt charge is stored in the capacitor. In connection with the selection of these circuit elements, patient impendance is assumed to be about 50 ohms.
  • the circuit illustrated in FIGURE 1 may be operated as follows: the switch 4 is closed causing the capacitor 6 to be charged to a value determined by the voltage of the source and the duration of the switch closure. The switch 4 is then opened and switch 8 closed. When the switch 8 is closed the charge on the capacitor 6 is applied to the series circuit of thermistor 10 and load 12. Initially, the resistance of the thermistor 10 is relatively high so that the current to the load 12 is relatively low. However, the initial current flow causes the temperature of the thermistor to rapidly increase, thereby lowering its resistance ad causing the current flow through the thermistor to increase. The temperature of the thermistor continues to rise with increases over time in current flow.
  • the rate of change of resistance of the thermistor, and hence the change in magnitude of the current delivered by the pulse, illustrated by waveform K in FIGURE 2, is determined by the temperature/resistance characteristics of the selected thermistor and by the heat capacity of the thermistor selected.
  • the temperature of the thermistor will continue to rise until a maximum value of current flow is reached, which value is determined by the amount of the charge on the capacitor 6. As the capacitor continues to discharge through the thermistor and load 12, the current through these elements is reduced.
  • FIGURE 2 This effect of thermistor 10 on current flow delivered by the pulse is illustrated graphically in FIGURE 2, where the current through the load is plotted against time.
  • the current through the load 12 jumps to a finite value that depends on the initial resistance of thermistor 10 and load 12.
  • the switch 8 remains closed the current continues to increase until a maximum value is reached. This increase is due to the decreasing resistance of thermistor 10.
  • the charge on the capacitor 6 is decreasing and at a certain point the current through the load reaches a maximum value and then decreases.
  • the resultant current waveform identified at K in FIGURE 2 may be described approximately as a damped sinusoidal wave.
  • FIGURE 3 The circuit illustrated in FIGURE 3 is identical to the circuit illustrated in FIGURE 1 and described above, except that a second thermistor 14 is connected in parallel with the load.
  • the thermistor 14 has a negative coefficient of resistance so that the current through it will increase as the temperature of the thermistor increases.
  • three series connected thermistors of the type manufactured by Keystone Carbon Company of St. Mary's, Pennsylvania and identified by model No. CL-70 may be satisfactorily used as thermistor 14.
  • FIGURE 4 The effect of the circuit illustrated in FIGURE 3 on current flow delivered by the pulse is illustrated in FIGURE 4, where once again current through the load is plotted against time.
  • the interaction of thermistor 10 and the load occurs in substantially the same manner a with the circuit illustrated in FIGURE 1.
  • the value of thermistor 14 is much larger than the load resistance, so that most of the current flows through the load during initial portions of the pulse, as illustrated in current waveform L.
  • thermistor 14 heats, its resistance decreases, and the thermistor begins to shunt current away from the load.
  • the resistance of thermistor 14 is much less than the resistance of the load, and as a result the thermistor shunts away from the load almost all of the remaining energy in the capacitor.
  • thermistor 14 may be employed in a conventional RLC circuit to perform the shunting function described above in connection with the circuit illustrated in FIGURE 3.
  • FIGURE 3a illustrates a conventional RLC circuit in which thermistor 14 is connected in parallel with the load so as to shunt residual portions of the energy discharged by capacitor 6 away from the load, as described above with respect to the circuit illustrated in FIGURE 3.
  • the circuit illustrated in FIGURE 3a differs from the circuit illustrated in FIGURE 3 only in that inductor 15 is used in place of thermistor 10.
  • the current flow of the pulse delivered by the circuit illustrated In FIGURE 3a will rise and fall substantially in accordance with waveform L illustrated in FIGURE 4, except that the current will rise from a lower initial magnitude.
  • circuit 30 illustrated in FIGURE 5 was developed.
  • Circuit 30 is identical to the circuit illustrated in FIGURE 1, except that it includes an inductive element 32 connected in series between switch 8 and thermistor 10.
  • inductive element 32 is a 10mH inductor.
  • the amplitude of the current delivered by the pulse generated by circuit 30 increases more slowly than does the amplitude of the current delivered by the pulses generated by the circuits illustrated in FIGURES 1 and 3. Under certain conditions, this slower increase in the amplitude of the current delivered by a pulse is desired. For instance, when circuit 30 is incorporated in a defibrillator and the pulse the circuit generates is to be delivered to a patient for the purpose of defibrillating the patient's heart, for certain medical conditions it may be desirable that the current delivered by the pulse not increase too rapidly toward a peak value.
  • inductive element 32 may be employed in the circuit illustrated in FIGURE 3.
  • the inductive element 32 is also connected in series between switch 8 and thermistor 10.
  • Circuit 30 illustrated in FIGURE 5 is slightly heavier and more expensive than the circuits illustrated in FIGURES 1 and 3 due to the inclusion of inductive element 32. However, the circuit does not weigh as much or cost as much as conventional RLC pulse forming circuits which typically include at least one inductive element rated at between 20mH and 50mH. In certain circumstances, an ideal balance between weight and cost savings versus circuit performance may be achieved by using circuit 30 illustrated in FIGURE 5 in place of the circuits illustrated in FIGURES 1 and 3 or in place of conventional RLC circuits.
  • thermistors 10 and 14 in the circuits illustrated in FIGURES 1, 3, and 5 and described above will retain sufficient residual heat between pulses as to prevent the circuits from generating pulses having the current waveform illustrated in FIGURES 2, 4, and 6 and described above.
  • the extent to which the thermistors retain residual heat will vary as a function of the frequency of the pulses, the temperature/resistance characteristics of the thermistors, and the environment in which the thermistors are located.
  • heat sinks 50 may be attached to thermistors 10 and 14.
  • Each heat sink 50 includes a plurality of planar fin members 52 which are attached via integral base plate 53 to the front and back surfaces of the thermistor. Such attachment is achieved using a heat conductive bonding agent 54, such as a suitable epoxy.
  • Heat sinks 50 are made from a material having a high thermal conductivity, such as aluminum. By adding heat sinks 50 to thermistors 10 and 14, the latter will cool rapidly, typically in less than about five seconds, thereby allowing rapid application of pulses.
  • FIGURES 9 and 10 recently experimental and clinical tests have been performed using defibrillators designed to produce a defibrillation pulse having a biphasic or alternating polarity waveform.
  • This waveform is characterized by the first portion of the pulse having a positive polarity and the second portion of the pulse having a negative polarity, much like the waveform N illustrated in FIGURE 10.
  • Circuit 70 is similar to the circuit illustrated in FIGURE 1 in that it comprises voltage source 2, switches 4 and 8, and capacitor 6. Additionally, the resistive load with which circuit 60 is designed to be connected is represented by resistive element 12. One side of resistive element 12 is identified by reference numeral 66 and the other side of the resistive element is identified by reference numeral 68. Circuit 60 differs from the circuit illustrated in FIGURE 1 in that it includes thermistors 72, 74, 76 and 78 in place of thermistor 10. Thermistors 72 and 78 are positive temperature coefficient thermistors and thermistors 74 and 76 are negative temperature coefficient thermistors.
  • Thermistors 72-78 are coupled with resistive element 12 in a bridge-like configuration, with thermistor 72 being connected between switch 8 and side 66 of resistive element 12, thermistor 74 being connected between switch 8 and side 68 of resistive element 12, thermistor 76 being connected between side 66 of resistive element 12 and the negative polarity side of voltage source 2, and thermistor 78 being connected between side 68 of resistive element 12 and the negative polarity side of voltage source 2.
  • Thermistors 72-78 are selected so that the resistance of thermistor 74 is less than the resistance of thermistor 72 when the thermistors are at ambient temperature, e.g., 25° C, and so that the resistance of thermistor 76 is less than the resistance of thermistor 78 when these thermistors are at ambient temperature.
  • the thermistors are selected so that thermistors 74 and 76 have nearly identical resistance across substantially the entire temperature spectrum at which they will operate, and so that thermistors 72 and 78 have nearly identical resistance across substantially the entire temperature spectrum at which they will operate.
  • thermistors 72-78 when the latter are at ambient temperature, and when switch 8 is closed, current will flow from capacitor 6 along current path i P1 (FIGURE 9) which flows through thermistor 74, resistive element 12 (i.e., the resistive load), and then thermistor 76.
  • This current flow through thermistors 74 and 76 causes the thermistors to heat rapidly with the result that their resistance increases rapidly.
  • the amplitude of the current delivered through thermistors 74 and 76 to the resistive load decreases with time, as illustrated in FIGURE 10.
  • the biphasic waveform N illustrated in FIGURE 10 may be generated.
  • the specific configuration of waveform N may thus be precisely tailored to the application in which circuit 60 is to be used by appropriate selection of thermistors 72-78.
  • capacitor 6 was a 50 microfarad capacitor which was changed to 4,320 volts
  • the resistive load was 50 ohms
  • thermistors 74 and 76 had a resistance of 500 ohms at 25° C and a heat capacity of 0.5 joules/°C
  • thermistors 72 and 78 had a resistance of 2 ohms at 25° C, a heat capacity of 0.6 joules/°C and a transition temperature of 65° C.
  • the load had a resistance of about 50 ohms.
  • Heat sinks 50 may also be attached to thermistors 72-78 in the manner described above with respect to thermistors 10 and 14. Such use of heat sinks 50 is appropriate when it is desired to increase the rate at which the thermistors 72-78 cool down after heating.
  • FIGURES 1, 3, 3a, 5, and 9 may be advantageously incorporated in a known manner in a conventional defibrillator 100 of the type disclosed in U.S. Patent No. 3,814,105 to Howard et al. and illustrated schematically in FIGURE 11.
  • switches 4 and 8 of the circuits illustrated in FIGURES 1, 3, 3a, 5, and 9 are coupled, respectively, with charge button 102 and discharge button 104.
  • the resistance 12 of the circuits illustrated in FIGURES 1, 3, 3a, 5, and 9 is provided by a patient (not shown) connected to electrodes 106 and 108. It is to be understood that defibrillator 100 includes all the other controls and displays of a modern defibrillator.

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  • Health & Medical Sciences (AREA)
  • Cardiology (AREA)
  • Heart & Thoracic Surgery (AREA)
  • Engineering & Computer Science (AREA)
  • Biomedical Technology (AREA)
  • Nuclear Medicine, Radiotherapy & Molecular Imaging (AREA)
  • Radiology & Medical Imaging (AREA)
  • Life Sciences & Earth Sciences (AREA)
  • Animal Behavior & Ethology (AREA)
  • General Health & Medical Sciences (AREA)
  • Public Health (AREA)
  • Veterinary Medicine (AREA)
  • Physics & Mathematics (AREA)
  • General Physics & Mathematics (AREA)
  • Electrotherapy Devices (AREA)
  • Amplifiers (AREA)
  • Oscillators With Electromechanical Resonators (AREA)
  • Optical Head (AREA)
  • Generation Of Surge Voltage And Current (AREA)

Claims (11)

  1. Instrument médical servant à délivrer une impulsion d'énergie électrique à un patient, ledit instrument médical comprenant une source d'énergie (2), un dispositif (6) de stockage d'énergie, une paire d'électrodes pouvant être fixées au patient et un moyen de connexion pour coupler l'énergie stockée dans le dispositif de stockage d'énergie à la paire d'électrodes, caractérisé par une thermistance (10) branchée entre le dispositif de stockage d'énergie et la paire d'électrodes pour faire varier au cours du temps un signal de courant qui peut circuler du dispositif de stockage d'énergie à la paire d'électrodes afin de produire un signal de courant de défibrillation qui varie en fonction de la température de ladite thermistance.
  2. Instrument médical selon la revendication 1, dans lequel ladite thermistance (10) est en outre caractérisée par une valeur ohmique qui diminue proportionnellement à l'augmentation de température.
  3. Instrument médical selon la revendication 2, dans lequel ladite thermistance a un coefficient de température négatif
  4. Instrument médical selon la revendication 1, dans lequel ledit moyen de connexion est en outre caractérisé par :
    (a) un premier interrupteur (4) branché entre la source d'énergie et le dispositif de stockage d'énergie afin de, sélectivement, coupler la source d'énergie avec le dispositif de stockage d'énergie ou ne pas les coupler, et
    (b) un deuxième interrupteur (8) branché entre le dispositif de stockage d'énergie et le moyen de connexion afin de, sélectivement, coupler le dispositif de stockage d'énergie avec la paire d'électrodes ou ne pas les coupler.
  5. Instrument médical selon la revendication 1, caractérisé en outre par un shunt (14) branché audit moyen de connexion pour détourner du patient une partie résiduelle de l'énergie délivrée par ledit dispositif de stockage d'énergie quand le dispositif de stockage d'énergie est couplé à la paire d'électrodes, ladite partie résiduelle ayant une valeur qui est fonction de la température dudit shunt.
  6. Instrument médical selon la revendication 5, dans lequel ledit shunt (14) comprend une thermistance dont la valeur ohmique varie en fonction de la température de la thermistance.
  7. Instrument médical selon la revendication 6, caractérisé en outre en ce que ladite thermistance a un coefficient de température négatif.
  8. Instrument médical selon la revendication 1, caractérisé en outre par un puits de chaleur (50) couplé à ladite thermistance pour dissiper la chaleur provenant de ladite thermistance.
  9. Instrument médical selon la revendication 8, dans lequel ledit puits de chaleur comprend une pluralité d'ailettes en aluminium.
  10. Instrument médical selon la revendication 1, caractérisé en outre par une inductance (15) branchée entre le dispositif de stockage d'énergie et la paire d'électrodes pour retenir et libérer une quantité prédéterminée d'énergie délivrée lors du branchement du dispositif de stockage d'énergie à la paire d'électrode afin d'augmenter le temps nécessaire pour que l'énergie délivrée à la paire d'électrodes atteigne une valeur de pic.
  11. Instrument médical selon la revendication 1, caractérisé en outre par des première et deuxième thermistances (74, 76) pouvant être branchées à la paire d'électrodes du patient afin de définir un premier trajet de courant, et des troisième et quatrième thermistances (72, 78) pouvant être branchées à la paire d'électrodes du patient afin de définir un deuxième trajet de courant, lesdites première et deuxième thermistances ayant un coefficient de température positif et lesdites troisième et quatrième thermistances ayant un coefficient de température négatif, de sorte que le courant de défibrillation suit le premier trajet de courant puis le deuxième trajet de courant.
EP92910606A 1991-04-12 1992-04-10 Circuits de formation d'impulsion Expired - Lifetime EP0717644B1 (fr)

Applications Claiming Priority (3)

Application Number Priority Date Filing Date Title
US07/685,132 US5275157A (en) 1991-04-12 1991-04-12 Pulse forming circuits
PCT/US1992/002993 WO1992018196A1 (fr) 1991-04-12 1992-04-10 Circuits de formation d'impulsion
US685132 2003-10-14

Publications (3)

Publication Number Publication Date
EP0717644A4 EP0717644A4 (fr) 1996-02-19
EP0717644A1 EP0717644A1 (fr) 1996-06-26
EP0717644B1 true EP0717644B1 (fr) 1998-09-09

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EP92910606A Expired - Lifetime EP0717644B1 (fr) 1991-04-12 1992-04-10 Circuits de formation d'impulsion

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US (2) US5275157A (fr)
EP (1) EP0717644B1 (fr)
JP (1) JPH06507090A (fr)
AT (1) ATE170768T1 (fr)
AU (1) AU1765792A (fr)
CA (1) CA2104954A1 (fr)
DE (1) DE69226970T2 (fr)
WO (1) WO1992018196A1 (fr)

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Also Published As

Publication number Publication date
EP0717644A4 (fr) 1996-02-19
WO1992018196A1 (fr) 1992-10-29
US5275157A (en) 1994-01-04
DE69226970D1 (de) 1998-10-15
CA2104954A1 (fr) 1992-10-13
ATE170768T1 (de) 1998-09-15
AU1765792A (en) 1992-11-17
DE69226970T2 (de) 1999-03-11
JPH06507090A (ja) 1994-08-11
US5370664A (en) 1994-12-06
EP0717644A1 (fr) 1996-06-26

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